This is a shared instrumentation grant application for a multiparameter fluorescence activated cell sorter, the FACStar Plus. This instrument has 1) dual laser excitation; 2) improved emission optics for four color fluorescence detection and two angle light scatter detection; 3) an extremely rapid sorter logic for high resolution cell sorting at high flow rates; 4) advanced pulse signal processing allowing for eight parameter list mode data collection from any of 49 available parameters; 5) a powerful computer interface with a Digital micro-VAX, permitting non- orthogonal sort window gating in n-dimensional space; 6) six high performance photomultiplier tubes; and 7) eight log/linear amplifiers. This instrument will provide us with state-of-the-art flow cytometry and serve as an invaluable resource for the PHS- supported research at the Research Institute of the Scripps Clinic.